Direct or indirect impact of a hand, often in the clenched fist position, with an object, regardless of the hardness or density of the object, can result in injury because of the detrimental forces acting on the anatomical configurations of the hand. Such impact frequently produces forces sufficient to cause injuries to one or more metacarpophalangeal joints (MPJ) (commonly termed the "knuckles") or carpometacarpal joints (CMCJ) of any finger of the hand, or the thumb, or the carpal bones or the distal radio ulnar joint (DRUJ).
When repeated impact of the hand with an object occurs, for example, in contact sports such as boxing or in performing occupational duties such as law enforcement or military service, injuries of the hand are more likely to occur and can severely hamper or totally prevent use of the hand. The adverse effect of hand injuries on performance is nowhere more profound than in boxing because the recurrent high energy forces generated by the hand's clenched-fist striking a target, coupled with its vulnerable anatomical configurations, predisposes it to predictable and disabling injuries. The flawless punching mechanics, unparalleled hand speed, coordination, and strength of the skillful boxer are thus prone to compromise. Furthermore, the hands are the boxer's principal means of defense because they are used to counterpunch and to block incoming blows. Thus, when hand injury occurs, both offensive and defensive capacities diminish and the boxer becomes vulnerable to further injury.
A boxer's hands are the tools of his trade. However, like all tools, boxers' hands are prone to mechanical failure. Indeed, corroborating a long-standing impression among sports medicine experts, evidence is accumulating that hand injuries in boxing may constitute a sport-specific epidemic.
The most serious hand injury encountered among boxers, which can result from direct blows to the knuckles of a clenched-fist, is metacarpophalangeal joint damage, including extensor mechanism disruption, either partial or complete, termed the "Boxer's Knuckle," due to its prevalence in boxing. Other common injuries of the metacarpophalangeal joints are digital fractures, capsular tears, collateral ligament disruptions, and articular fractures. These injuries often occur at the long finger knuckle due to its vulnerable protrusion as well as an anatomical predisposition, however, these injuries also occur at the other knuckles with considerable frequency.
The relaxed or gently clenched fist within a boxing glove, unexposed to compressire forces, demonstrates mild to moderate flexion of the metacarpophalangeal joints. In contrast, the impact caused by a forceful punch causes the clenched-fist to considerably alter its contours. The metacarpophalangeal joints are forced into acute flexion, almost to a degree of subluxation, and overlying extensor mechanisms along with adjacent joint capsules and collateral ligaments are stretched to maximum tension across the dorsally prominent metacarpal heads. The metacarpophalangeal joints, especially those of the protrusive, more vulnerable index and long fingers, are protected only by a thin envelope of skin and subcutaneous tissues, and thus are prone to serious damage when subjected to the excessive forces generated by boxing.
The extensor mechanism includes a stout central tendon and less substantive transverse, peripheral fibers, termed sagittal bands, stabilizing the central tendon and spanning the radial and ulnar margins of the joint. The intact extensor mechanism permits unimpaired metacarpophalangeal joint motion and by virtue of its broad fibrous configuration provides a protective cover for the underlying articular structures. Conversely, extensor mechanism disruption compromises metacarpophalangeal joint function and also increases the risk of additional injury to unsheathed subjacent articular components.
Extensor mechanism injury of the metacarpophalangeal joint (MPJ) reveals a characteristic spectrum of pathology. Most commonly the sagittal band, either radial or ulnar, demonstrates a tear adjacent to the central tendon; less frequently, the central tendon splits longitudinally. The most extensive lesion, apt to result from a force causing both extreme flexion and ulnar deviation of the knuckle, is a complete rupture of the radial sagittal band with ulnar dislocation of the central tendon. Profound joint swelling, compromised metacarpophalangeal joint extension, often with an extensor lag, and central tendon dislocation or subluxation with a palpable and exquisitely tender tissue defect at the site of rupture, are characteristic features of the complete rupture. This major disruption invariably occurs in association with a massive capsular tear and requires prompt repair for restitution of soft tissue integrity and preservation of joint function.
Variation in the basic closed fist mechanism of injury accounts for the proclivity of injury at other specific anatomical sites. Either a violent blow just proximal to the knuckle or an axial force transmitted proximally along the metacarpal shaft is liable to disrupt and destabilize the carpometacarpal joints, usually those of the vulnerable index and long fingers. The carpometacarpal joints of these digits are characterized by precision-fit bony contours and strong capsular ligaments serving to bind tightly the metacarpal shafts to the wrist. While this rigid configuration creates a sturdy central column affording skeletal stability and strength necessary for normal hand function, the inflexible, unyielding structure of the index and long carpometacarpal joints renders them highly susceptible to injury from recurrent high-energy forces generated by continuous punching. These small joints, although well suited for diffusing the majority of compression forces applied to the hand during routine usage, cannot easily withstand the stress imposed by boxing and are prone to deterioration.
An isolated episode of trauma can cause a serious carpometacarpal (CMC) sprain. Repeated injury often results in progressive joint derangement with formation of a characteristically painful mass of hypertrophic bone overlying the carpometacarpal juncture, descriptively termed traumatic metacarpal bossing. In some cases chronic instability leads to obliteration of these critical joints and disabling traumatic arthritis.
The classic boxer fracture, which despite common belief is an infrequent occurrence among competitive boxers, involves the small finger metacarpal neck or metaphysis and often results from a haphazard or "sloppy" punch. Far more prevalent is fracture of the index, long, and ring finger metacarpal shaft, or diaphysis. Contingent on the multi-directional forces of injury causing angular, rotatory, and axial displacement, the configuration of these fractures may be transverse, oblique, or spiral-oblique. A direct force on the dorsal surface of the tightly clenched fist is apt to cause a transverse fracture plane resulting in dorsal angulation with a clearly visible prominence of the proximal fracture fragment. A major angular component of injury, usually due to a misdirected blow, causes the oblique or spiral-oblique fracture-often resulting in a conspicuous rotational deformity with overlapping of the injured and adjacent digits.
With all displace metacarpal fractures, a consistent deformity, and one requiring prompt correction, is excessive bony shortening. Failure to restore critical metacarpal length and the normal contour of the metacarpal head is liable to result in a serious compromise of punching mechanics and boxing skills. Indeed, seemingly minimal disturbances in metacarpal alignment--as little as 5 degrees of malrotation, 20 degrees of dorsal angulation, or 3 millimeters of shortening--can lend to considerable deformity with major dysfunction unless detected and corrected.
In addition, the prominent position and rigidity of the second and third metacarpals make them particularly susceptible to bending torques applied over the dorsal aspect of the metacarpal heads during forced palmar flexion of the wrist when the fingers are not in a position to dissipate the applied force.
The thumb, in contrast to the rigid central digits, is a highly mobile unit with inherent instability and vulnerability owing to a paucity of strong ligamentous attachments as well as the absence of protective border digits. This configuration subjects the thumb to detrimental forces in various planes. Hyperextension and angular forces are apt to disrupt the collateral ligaments of the metacarpophalangeal joint, whereas axial compression is the deleterious mechanism of fracture, dislocation, or fracture-dislocation of the carpometacarpal joint. Thus, the thumb is most vulnerable to collateral ligament rupture of the metacarpophalangeal joint and carpometacarpal fractures or fracture dislocation.
Conventional attempts to prevent these hand injuries, and reduce the incidence of further injury during rehabilitation, have utilized various methods in attempts to protect the hand during activities in which there is a potential of injury from blunt trauma to the hand. One conventional device which attempts to prevent injury to the hand is a bandage formed by wrapping muslin or a similar material and tape around portions of the hand. For example, the rules of Olympic competition permit wrapping areas of each hand with only one yard of muslin bandage. Another approach utilizes custom-fit, molded casts or structures which cover the metacarpophalangeal joints. These approaches do not protect against the forces which are transmitted to common sites of injury. Still another conventional method is the use of padding or a balloon placed over an injured knuckle to attempt to deflect force away from a damaged metacarpophalangeal joint. These approaches suffer from several disadvantages. Since they are not fabricated in accordance with rational protection against predictable forces imposed on these sites, well recognized for their vulnerability to injury, and since they are not designed to minimize excessive motion of the joint, these ill conceived bulky bandages, casts, or padded structures afford little protection to the hand because they do not provide the necessary impact attenuation. This is especially so in the case of the more compact bandage sanctioned for Olympic competition. Furthermore, conventional hand protection devices do not stabilize the joints so as to reduce the risk of carpometacarpal and metacarpophalangeal joint injury and subluxation dislocation.